All the summons are rather useful for me. And it's really easy to max out their levels (since they all share levels) with Stitch, and raises their summon gauge to 9. Chicken Little and Stitch actually help you in battle. Chicken Little will smack the enemy with a ball every once in a while, or he will whistle and call all the enemies into one spot (rather useful). Stitch will occassionally shott the enemy or play his ukulele and make the enemies drop HP orbs. Genie won't do anything to the enemy, but he will restore you MP, which makes him awesome. Peter allows you to fly, but the only the he'll do by himself is have Tinkerbell revive you if you lose all your HP, which is only slightly useful. Genie and Peter Pan's limits however are rather powerful. I use Genie for MP restoration and then dismiss him, and I use Chicken Little to make a pair of Crimson Jazz a bit easier, but I use them the most during the Titan Cup.